Thanks, but I don't really know what you mean by backstairs, as most apartments I know just open to the one staircase. It's not way thin, but I'm just saying most of the ones in my city were wider and thicker. The ones which exist, that is. There's only some of them left in the center and other apartment buildings are basic concrete shits.
My point is rather that it needn't be a bank or anything like that to be somewhat fancy, that used to be in style... some time. Early 20th century, maybe?